The present disclosure relates to a current resonant power supply device, and particularly relates to a current resonant power supply device, which can achieve reduced power consumption under light load.
Japanese Patent Application Publication No. 2014-60895 (Patent Literature 1) and Japanese Patent No. 5384973 (Patent Literature 2) disclose current resonant power supply devices that can achieve reduced power consumption under light load.
The current resonant power supply device of Patent Literature 1 judges whether the device is currently in a light load state by comparing a power value detected by the power detection circuit with threshold Vref. Patent Literature 1 discloses a burst oscillation operation that may be performed while controlling the cycle of the burst oscillation if it is judged that the device is currently in the light load state.
The current resonant power supply device of Patent literature 2 detects the phase of current flowing through the switching elements. If the phase of the detected current is smaller than a predefined value, the current resonant power supply device judges that the device is currently in a light load state, and operates in a burst oscillation mode while operating the high side switch and the low side switch at unequal duty ratios.
Meanwhile, when changed to a standby load state, an Inductor Inductor Capacitor (LLC) current resonant system receives a standby signal generated externally, and switches from a normal operation state to a standby state.
Specifically, the standby signal is outputted from a system microcomputer on the secondary side of a transformer and is inputted into a power control integrated circuit (IC) on the primary side of the transformer via a photocoupler. For example, an SB (standby) terminal of the power control IC on the primary side of the transformer receives the standby signal from the photocoupler on the secondary side of the transformer.
The current resonant power supply devices of Patent Literatures 1 and 2 are capable of transitioning to a burst mode upon detection of a light load state.
U.S. Patent Application Publication No. 2016/0065075 (Patent literature 3) discloses a current resonant power supply device that comprises a first switch and a second switch connected in series to both terminals of a DC power source; a series circuit comprising a reactor, a primary winding of a transformer, and a capacitor connected in series, and connected to a node between the first and second switches and first terminal of the DC power source; a rectifier smoothing circuit that rectifies and smoothens a voltage generated across a secondary winding of the transformer and outputs a DC voltage; a control circuit that alternately turns the first and second switches on and off; a voltage detection circuit that detects the DC voltage from the rectifier smoothing circuit; a signal generation circuit that generates a feedback signal based on the DC voltage detected by the voltage detection circuit, and outputs the feedback signal, the feedback signal being for turning the first and second switches on and off; a load current detection circuit that detects load current contained in resonance current flowing through the capacitor; a standby state detection circuit that detects a standby state based on the load current detected by the load current detection circuit and a standby threshold; and a burst oscillation circuit that operates the first and second switches in a burst oscillation mode based on the feedback signal if the standby state is detected.